Automatic equalization device and method of starting-up the same

Details Automatic equalization device and method of starting-up the same Automatic equalization device and method of starting-up the same

1983-08-17

1986-02-18

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

333 18, H04B 306, H04B 310

Patent

active

045717338

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to an automatic equalization device provided in a modem in a receiver in a digital data transmission system and to a method of starting-up the automatic equalization device, particularly a method for starting-up an automatic equalization device at a high speed.
In a multipoint communication system, a master station communicates selectively with one of a plurality of the slave stations. A transmitter and a receiver of the master station are connected through a telephone transmission line with receivers and transmitters of the slave stations. In such a type of communication system, the transmitter of the master station is always connected in an on-line manner with the receivers of the slave stations. The master station polls each of the salve station in sequence. Such a polled slave station transmits an "acknowledgement" signal in response to a received "request for transmission" signal and subsequently transmits the data if the slave station has data to be transmitted.
It is necessary for a modem to adjust its receiver characteristics to the characteristics of the telephone transmission line prior to the actual receipt of data from one of the slave stations. The characteristics of the telephone transmission line vary for each slave station, primarily because of the change of distance between the master station and slave stations. Once the receiver is adjusted to the telephone transmission line, it is possible to satisfactorily track the change of line characteristics using known, relatively slow speed methods. However, when the receiver first receives the training data, there is a great difference in the characteristics of the receiver and the characteristic of the line. Under such start-up conditions, it takes about 2 seconds to adjust the receiver to the line by the known, relatively slow speed tracking method. The total adjustment time for one request for transmission equals the unit adjustment time multiplied by the number of the slave stations. This total adjustment time is a key factor which significantly reduces the efficiency of data transmission in prior art systems.
Various proposals have been made to provide a special start-up procedure to facilitate the quick adjustment of the receiver to the telephone transmission line. Typical of these is the transmission from the transmitter of a special signal series by which the receiver can derive a signal having the characteristic of the telephone transmission line for the receiver itself. In accordance with this special signal series, a timing error signal and a phase error signal are generated. Using these, an equalization device or the like in the receiver is started up.
As the signal series, i.e., the training signal for the start-up of the equalization device CCITT recommendations prescribe the transmission of a binary pseudo random data code (hereinafter referred to as a PN code). Hence, various methods have been proposed in which, to initialize the correction coefficient (tap coefficient) of the equalization device from the PN code, the correlation between the data and the error signal is calculated and used to correct and determine the tap coefficient. However, such methods have disadvantages of requiring a large, complicated circuit for calculating the correlation and requiring a considerably long time for determining the tap coefficient of the equalization device. For example, about 250 msec are required from a request for transmission to the transmission of the data.
U.S. Pat. No. 3,962,637 to David M. Motley et al. proposed a method for the high-speed start-up of an equalization device in a receiver. In this U.S. patent, a special signal comprising the three segments mentioned below is used for the training signal for the start-up of the equalization device.
That is, in the first segment, a tone signal obtained by modulating a carrier signal in a predetermined phase and amplitude is transmitted. In the second segment, a signal obtained by modulating the carrier signal by the data serie

REFERENCES:
patent: 4047013 (1977-09-01), Milewski
patent: 4089061 (1978-05-01), Milewski
patent: 4430743 (1984-02-01), Watanabe
patent: 4441192 (1984-04-01), Kita et al.

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